when I use a input node, and point it to the height.tif from WorldB I DO get a downstream relative path:

WorldB\output\height.tif

There are a couple of issues and problems with this workflow,if you are trying to build modular and automate world building:

Data portability: If I copied the c:\dev\worldmachine folder to another drive like D: the path is no longer valid, as it's absolute instead of relative. Think build machines, source control, multiple users, workspaces and depot mapping ... this will eventually be encountered.

Modularity: I have to always order reuse in a downstream way. Eventually this will be a mess and become inflexible.